Tree Protection during Construction
by Kim Ley
Warmer weather is hopefully coming to town in our not too distant future, so Rooted in Cheyenne (RIC) would like to share some tips with home and business owners on how to protect new and existing trees during construction season. RIC has emphasized the importance of shade trees to our local community’s health, quality of life, and property values. New and established shade trees add value to residential and commercial properties which is why it is important to take precautionary measures if construction is taking place around planted trees.
Before construction begins it is important to determine which trees to preserve. Have a licensed arborist evaluate the health of mature trees as some large, mature trees may not be structurally sound or esthetically appealing to warrant preservation.
There are four general forms of direct tree injury that can be caused by mechanized equipment: bark removal, branch breakage, surface grading and trenching injury. Bark removal can be caused by any type of equipment. Modern construction equipment can quickly damage tree bark. Damage to the bark of a tree can leave the tree more susceptible to damage from insects and environmental conditions. Make sure no one operates equipment within the area under the branches of trees to be saved. This area under the branches is called the tree dripline. Surface grading removes surface vegetation and topsoil that contain many critical for tree survival. Also, injury to the tree base can often occur in conjunction to surface grading. Trenching for utilities can cause substantial root damage and should be done far away from existing trees. If trenching is unavoidable, place the trench as far from the trunk as possible (minimum 2.5 meters or 8 feet), so as to cut as few roots as possible. Cleanly prune cut roots and refill trenches as soon as possible to prevent excessive moisture loss. Wounds make the tree highly susceptible to root pathogens and decay fungi. Decline and death of the tree can result if more than 40 percent of the stem or roots are damaged. Stressed trees are also more susceptible to insects such as bark beetles and borers.
Shade tree damage prevention is less costly than damage correction. Contracting companies and homeowners working on their own projects can take steps to protect trees from potential damage. Some of those steps include:
Mark the areas to protect. Brightly colored temporary fences/barricades put up around the trees to preserve alert all parties involved in construction of areas that should be kept clear of equipment for the safety of the tree. The size of the barriers can vary based on tree species and size. For recently planted trees (one to four years), the area under the branches (dripline) should be sufficient. For older more mature tree specimens, barricades should extend beyond the dripline; for each 1 inch of trunk diameter, extend the protection area an additional foot.
Avoid soil fill and compaction. After a tree is established, any activity that changes the soil condition is extremely detrimental to its health. Construction traffic tends to compact soil most severely near the surface, the area where the majority of tree roots reside. Soil compaction decreases surface and subsurface drainage and can interfere with essential gas exchange processes. When root growth is restricted by compacted soils, fewer nutrients and less water are available for plant growth. Conversely, if excessive amounts of soil are added around a tree base, the additional soil can interfere with normal air and moisture circulation to the roots. Soil fills subject roots to improper gas exchange and can lead to carbon dioxide or toxic gas buildup. These factors will limit root growth, reduce tree vigor and can cause tree death. Keep construction traffic and material storage away from tree root areas. Apply 4 to 6 inches of wood chips around all protected trees to help reduce the possibility of compaction. If replacing topsoil, it should be high in organic matter and have good drainage properties—it should not be clay.
Avoid soil cuts. Lowering the grade usually is less problematic than fills, but can be equally harmful. Where the grade has been changed near a tree, the most common damage is the complete severing of major roots in that area. This can cause decline, death or decrease the tree’s stability against high winds. To protect the tree, terrace the grade or build a retaining wall between the tree and the lower grade. Walls should encompass an area extending at least to the dripline.
Despite the best intentions and most stringent tree preservation measures, injury to trees may still occur. Trees may require several years to adjust to the injury it may sustain during construction. Trees with injured roots may show branch dieback quickly or within a few months after the initial injury. Prune dying branches to reduce insect and disease damage to the rest of the tree. It is better to wait until the tree exhibits branch die back to see how much to prune, rather than arbitrarily removing parts of the crown because of an assumption that the root system was damaged. If uncomfortable with pruning, in the event trees are actually damaged, consider hiring a licensed arborist to care for the injured trees.
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